a) Field of the Invention
The present invention relates to a motor having gears which comprises a gear mechanism such as a decelerating gear mechanism. It specifically relates to an improvement of a motor having gears, etc., with which unstable rotations of a rotor in the motor produced during start-up are stabilized in a predetermined direction.
It further relates to an ice maker using a motor having gears, which rotates at low speed and controls torque at a low level.
b) Description of the Related Art
Conventionally, there is a motor having gears which comprises a gear mechanism such as a decelerating gear mechanism and to which an AC sync motor is applied as a driving source. In such a motor having gears, the rotational direction of a rotor is not stable during start-up. In order to stabilize the rotational direction, a shading coil is added or a lever for preventing reversed rotations (as disclosed in JP Kokai S62-260541) is provided.
This conventional use of a shading coil or a lever for preventing reversed rotations brought an attendant complicated structure and also increased the number of components. This resulted in increased time required for assembling and increased manufacturing cost. In addition, a motor employing a lever for preventing reversed rotations generates a clashing noise with reversed rotations, that is, a clashing noise occurs between a projection unit of a rotor and the lever for preventing reversed rotations. This has been a problem when the motor is used in quiet circumstances.
A conventional ice maker using the above mentioned motor having gears is configured such that a boundary between ice and an ice making tray is melted by a heater provided at the ice making tray and an ice removing member is rotated to slide and drop ice from the ice making tray into an ice storage container.
Because the motor having gears includes a decelerating gear mechanism, the motor rotates at low speed and requires high torque. While the number of rotations is decreased at an output shaft portion, the torque at the output shaft is increased to rotate an ice removing member with a high torque for an infallible operation. With this, ice on the ice making tray is smoothly separated therefrom and dropped into the ice storage container.
In a conventional ice maker, however, the boundary between ice and the ice making tray is sometimes not completely melted by conducting heat from the heater at the ice making tray to melt the boundary. In addition, to simplify a switching control, one may want to actuate the motor having gears simultaneously with conducting heat from the heater. In such a case, at the beginning of rotation of the motor, regardless of the attempts of removing ice by the ice removing member, ice is not separated from the ice making tray because of the attachment of ice to the ice making tray. This results in interrupting the operation of the ice removing member. In other words, the output shaft of the motor having gears comes into a locked status (interrupted operation). Then, high torque is added to the gears in gear trains formed in the motor having gears, which may damage teeth.
Such a risk of damaging teeth is normal in a motor having gears, which requires to be rotated at low speed, because of tendency of producing high torque. For this reason, a motor having gears to which a conventional AC sync motor is applied is used in such a way that the gear is reinforced with additional cost, or, in contrast, the number of rotations is kept higher. An ice maker having a motor having gears attempts to solve the above problems by sufficiently melting ice with a heater, more precisely controlling conduction of the heater, or employing a large-size motor. These countermeasures, however, result in costing too much, decreasing efficiency in assembly, making a large device, or melting too much of the ice. On the other hand, an ice maker without these countermeasure is broken in a short period, and thus its usable life is short.